In the field of hydraulic valves, for example, there is frequently the problem of detecting the movement of a movable valve piston in the enclosure filled with a high-pressure fluid using a position measuring system. In the context of known systems, for example, a push rod attached to the valve piston is guided out of the housing and is coupled to a position measuring system, for example in the form of an LVDT system, situated outside of the housing. This is associated with the disadvantage that the sealing of the push rod leading out of the pressure chamber is complex and can also represent a weak point over the life of the valve. Another disadvantage is that the additional placement of a position measuring system outside of the housing enlarges the axial length of such hydraulic valves.